RE: statspack , LAG - does this look OK

Don't have time to look at your query and results in detail, but yes the concept is useful - I do the same thing regularly, just with some slightly different approaches. You might want to check out some of the scripts from Tim Gorman at http://www.evdbt.com/tools.htm - I think he's already done a lot of the work for you.  

Just a few things to watch out with statspack data - negatives are probably after system restarts, or sometimes counters wrap past their max values and go negative if the instance is up for a long time or has a lot of activity and time for long executions will all be accounted for in the period in which the query completes so this can skew your data.  

With 10g, hopefully you're using AWR instead of statspack, but only if you have the diagnostics pack license unfortunately.  

Regards,
Brandon

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